Ribbon resistor with supporting means

ABSTRACT

A continuous ribbon strip of stainless steel is fan-folded to provide a plurality of equally spaced, parallel uniform linear lengths connected by U-shape folds, and the sole support for the resistor comprises short projections loosely received in openings located along the apices of the U-shape folds with the supporting mechanism including end plates, bolts, supporting insulators and pin projections, providing floating support of the resistor element for free expansion and contraction. Air flow through the folds for effective convective cooling or forced ventilation is substantially unrestricted by the supporting elements.

United States ,Patent Griffes [54] RIBBON RESISTOR WITH SUPPORTING MEANSMilton W. Griffes, Madison, Ohio Harvey Hubbell Madison, Ohio Sept. 13,1971 Inventor:

Assignee: Incorporated,

Filed:

Appl. No.:

[451 Oct. 10,1972

Primary ExaminerE. A. Goldberg Attorney-Baldwin, Egan, Walling & Fetzer[5 7] ABSTRACT A continuous ribbon strip of stainless steel is fanfoldedto provide a plurality of equally spaced, parallel uniform linearlengths connected by U-shape folds, and the sole support for theresistor comprises short projections loosely received in openingslocated along the apices of the U-shape folds with the supportingmechanism including end plates, bolts, supporting insulators and pinprojections, providing floating support of the resistor element for freeexpansion and contraction. Air flow through the folds for effective [56]References Cited convective cooling or forced ventilation is substan-UNITED STATES PATENTS tially unrestricted by the supporting elements.

3,027,532 3/1962 DuBois ..338/316 X 8 Claims, 9 Drawing Figures -1"! -3-18 d -E l ..T- lli? QAIQ I T. I

PATENTEDUCI 10 I972 SHEET 1 BF 2 INVENTOR.

MILTON W. GRIFFES ATTORNEYS PATENTEU 10 I97? 3.697.923

sum 2 OF 2 FIGS 60W AFTO N E YS C & S f y m a m r r m W 1 2 O l Q M W R!m. l m N G H; 4 5 I I 4 M 3 h m .4 A3 w N W m r 3 m M E. -q m a 8 in mm 3 5 i 3 RIBBON RESISTOR WITH SUPPORTING MEANS An object of the presentinvention is to provide a continuous element high capacity resistor,compact in design and rugged for heavy-duty use such as found instarting, speed regulating and braking of electrical motors found insteel mils, foundries, mines and other industrial areas utilizingcranes, hoists, traction equipment and heavy-duty service equipment.

Other objects and advantages of the invention will be set forth in theaccompanying drawings and specification and the essential featuresthereof will be defined in the attached claims.

In the drawings,

FIG. 1 is a perspective view of a first embodiment of this invention;

FIG. 2 is a top plan view of the same;

FIG. 3 is a fragmental perspective view taken from the position of theline 3-3 in FIG. 1;

FIG. 4 is an enlarged fragmental sectional view taken along the line 4-4of FIG. 2;

FIG. 5 is a fragmental side elevational view of a modification of thefirst embodiment taken along the line 5-5 of FIG. 2 and showing one unitmounted on top of another;

FIG. 6 is a fragmental perspective view of a second embodiment of theinvention;

FIG. 7 is a top plan view of the same;

FIG. 8 is an enlarged fragmental sectional view taken along the line8-8.of FIG. 6; while FIG. 9 is a fragmental sectional view taken alongthe line 9-9 of FIG. 8.

Referring now to FIGS. 1 and 2, a continuous strip 10 of electricalresistive material is fanfolded to provide a plurality of equallyspaced, parallel uniform linear lengths 10a connected by U-shape folds10b. The preferred material for this embodiment of the invention is a 3inch to 4 It inch wide, continuous, A.I.S.I. type, 406 stainless steelelement.

The support means for the resistor element comprises two frame endportions l1 and 12 and shown here as portions of steel channels. Thesechannels have flanges 11a and 12a, respectively, perforated at 13 sothat a plurality of these units may be bolted together in a verticalstructure. Between the frame end portions, a plurality of electricallyinsulating blocks 14 are assembled on each side of the resistor close tothe U-shape folds thereof on rods or bolts 15, each of which extends thefull length of the resistor and beyond the webs 11b and 12b of the frameend portions. Each set of insulator blocks, 14 on one side of theresistor and 14 on the other side, is assembled along its associatedbolt 15 in end to end relationship, there being suitable openingsthrough the blocks to receive the bolts. Interengaging means is providedon the engaging ends of adjacent blocks for holding the blocks inregistration and to provide rigidity in the assembled structure. Asshown in FIG. 4, the interengaging means comprises ceramic pins ofcylindrical form, one above and one below the bolt 15, these pins beingreceived in suitable recesses 17 in blocks 14 or 14'. The insulatorblocks 14 and 14 are of high strength, inorganic and non-tracking in thesense that they will not carbonize under heat. In one embodiment, theblocks are made of a stone-like inorganic plastic, calciumalumino-silicate, made and sold under the trademark Rosite by RostoneCorporation of Lafayette, Ind. The insulator blocks are assembled on thebolts 15 as shown in FIGS. 1 and 2 and with end insulators 18 betweenthe last linear length 10a at each end of the resistor and the frame endportions 11 and 12. These end insulators are interlocked with the lastblock 14 or 14' as shown in FIG. 4 at 16 and are also provided withextending nubs 18a which extend through appropriate openings in theframe end portion webs 11b as clearly seen in FIG. 1. Preferably, theupper end 18b of the end insulators is sloped as shown in FIG. 1 so thatgraphite or other electrically conductive dust will not collect thereon,such as in steel mill use. With the parts thus described assembled onthe bolts 15, nuts 19 are threaded on opposite ends of each bolt andpulled up tightly against the outer faces of the frame end webs 11b tohold the parts assembled. Preferably, double jam nuts are used at 19.Insulating collars 20 are provided between the nuts 19 and the frame web1 1b as shown.

As best seen in FIGS. 2 and 3, two projections 21 are provided for eachU-shape fold 10b of the resistor ribbon, These projections lie on a lineparallel to the linear lengths 10a and extend axially of each U-shapefold at its apex. Each of these projections is received loosely in anopening provided through the U-shape fold which is supported. Also, atambient temperature a small space is provided, as shown at 22, betweeneach U-shape fold 10b and the associated insulator block 14 or 14' whichholds the supporting projections 21. Thus, each fold of the resistorribbon provides a floating support for the resistor element 10 for freeexpansion and contraction under changing heat conditions. Each of theprojections 21 is held in its associated insulator block in any suitablemanner. This could be accomplished by molding the pins into theinsulator material but in one form of this invention, each of the pins21 is a spring pin of known construction consisting of a hollow metalcylinder of spring characteristics having a single slot extendinglongitudinally from end to end of the pin. Such a pin can be compressedradially inwardly and entered into a receiving recess in the insulatorblock, after which release of the pin causes the spring characteristicsto expand the pin to hold it firmly in the insulator block.

The insulator blocks 14 and 14 are alike except for the changesnecessary in the blocks 14 to accommodate terminal attachment plates 23and 24. These plates are welded in line with certain of the parallellinear lengths 10a of the resistor, as desired. Each of these plates, asshown in FIG. 4, has a suitable opening for the passage of a bolt 15 andother openings to accommodate the ceramic pins 16. Also, at their outerends, there are suitable openings such as that shown at 25 in FIG. 1 toreceive bolts 26 which are utilized to secure wire connection terminals27.

Referring to FIG. 4, an insulator sleeve 28 surrounds bolt 15 whereverit passes through one of the plates 23 or 24 to prevent any shorting ofcurrent between folds of the resistor ribbon through the bolt 15. Theinterlocking structure between blocks 14 comprises ceramic pins 16 likethose shown in FIG. 4 but, of course, no insulating sleeve 28 is neededwhere there are no terminal plates 23 or 24.

A plurality of the units just described can be assembled if necessary,one on top of the other, by securing bolts through openings 13 of theframe end portions of the two units. This is satisfactory for convectionheating because in such cases the air may pass vertically between thefolds of the resistor ribbon and may enter or exit in the spaces betweenthe insulator blocks 14 and 14' of a lower unit and similar insulatorblocks of the next unit above. I

However, in the case of forced ventilation, a modification may beprovided as shown in FIG. 5. Here the construction of the upper andlower units is exactly like that heretofore described except withrespect to the insulator blocks 14 and 14. Here the insulator blocks 140and 140 extend above and below the resistor ribbons l and The blocks 140and 140 are shown as terminating at the same level as the flanges 11a,12a, and 1 la, 120'. Thus, when an upper and lower unit are stacked withtheir flanges 11a and 12a bolted to the flanges 11a and 12a below, theinsulator blocks 140 and 140' and the uninterrupted frame end portionwebs 11b and 12b, at right angles thereto, are secured in registrationso as to provide an open vertical tunnel through which air may be forcedto provide better cooling for the resistors 10. As is well known, suchforced ventilation will permit the resistors to be used at two to threetimes the current rating for convection cooling.

The second embodiment of this invention, shown in FIGS. 6 through 9, isquite similar in operation except the construction differs. A highcapacity resistor ribbon is fanfolded as in the first embodiment toprovide a plurality of spaced, parallel uniform linear lengths 30aconnected by U-shape folds 30b. The sole support for the resistorcomprises a plurality of vertically oriented plates 31, each havingstamped integrally therewith spaced vertical projections 32 which enterloosely into suitable openings provided through the U-shape folds of theresistor ribbon lying on a line parallel to the linear lengths 30a andextending axially of each U- shape fold 30b at its apex. At each end ofthe resistor element are frame end portions 33 and 34 and between them,on each side of the resistor, extend vertically spaced parallel supportbars 35. The construction along each support bar is the same so one onlyneed be described. Referring to FIGS. 8 and 9, each bar 35 has anelectrically insulating tube or sleeve 36 surrounding it between theframe end portions. Mica is suitable for this sleeve. Between each pairof plates 31, a hollow steel tubular spacer 37 is provided and betweenthe spacer and the plate 31 on each side of the latter is provided firsta steel washer 38 next to the spacer and a mica washer 39 between thewasher 38 and plate 31. A similar structure is shown between each endplate 31 and a limiting spacer nut 40 threaded on the rod 35. Thisincludes a spacer 31' which abuts against an insulating collar of mica41 and between 31' and 41 and between 40 and 41 there is a steel washer38. Each of the bolts 35 passes through the web 33b or the web 34b ofthe frame end portions and is there secured firmly by nuts 42 and 43 onopposite sides. of the frame web. Between each of ths nuts 42 and 43 andthe associated end web is a suitable insulator 44 and a steel washer 45.

It will be noted that each of the plates 31, being rigidly supported bytwo of the bolts 35, allows no rocking of the plates 31 and theprojections 32 allow the resistor ribbon to float thereon with room forthe U- shape folds 30b to move back and forth on the projections 32under various changes of temperature.

As best seen in FIG. 7, suitable terminal plates 46 are welded in linewith certain of the linear resistor lengths 30a and the plates 46 aresupported on the bolts 35 in the same manner as indicated at 36, 37, 38and 39,-with respect to the plates 31.

Suitable bolt holes are provided at 33c and 34c so that flanges 33a and34a of one unit may be bolted to another similar unit vertically linedthereabove.

It should be noted that in both of the embodiments of this invention theprojections 21 of the first embodiment and projections 32 in the case ofthe second embodiment extend very slightly inwardly beyond the thicknessof the resistor ribbon, not more than a fraction of an inch, so thatvertilation between the folds of the resistor ribbon is substantiallyunrestricted.

In one form of this invention, the stainless steel resistor ribbon isfrom 3 k to 4 inches wide and the linear lengths 10a or 30a are betweenabout 8 and 10 inches long. The thickness of the ribbon per current tobe handled runs from about one thirty-seconds inch to three-sixteenthsof an inch when the current rating is between about amps. to 700 amps,respectively.

In the case of the second embodiment, one device utilized rods 35 of M;inch diameter surrounded by a mica tube 36 which was about one-sixteenthinch thick. In this embodiment, the support plates 31 were oneeighthinch thick.

Thus, this invention provides a fanfolded resistor which is uniquelysupported by metal pins or projections leaving the resistor element freeto expand and contract. It does not distort even under severe dutycycles. The construction is rugged throughout, the insulation system issuperior and the heavy welded terminals for circuit connections renderthis equipment suitable for heavy mill duty. The construction leaves thespace between the folds of the resistor substantially unobstructed forconvection or forced air cooling. There are no strip welds to causemechanical or electrical failures. The use of inorganic, non-trackinginsulating blocks insures insulation integrity even in conductive dustand moisture laden atmospheres.

I What is claimed is:

1. A support means for a continuous ribbon-type resistor fanfolded intoa plurality of equally spaced parallel uniform linear lengths connectedby U-shape folds, comprising a frame having portions at opposite ends ofsaid resistor opposite said linear lengths, supports connected betweensaid frame portions, one support extending crosswise of said fanfolds oneach side of said resistor, there being an opening through said ribbonresistor at the apex of each U-shape fold, projections carried by saidsupports, one projection opposite each of said openings, each of saidprojections being loosely received in its associated opening, meanselectrically insulating said resistor from said supports and from saidframe, and terminals attached to said resistor.

2. A support means as defined in claim 1, including two of said openingsbeing provided at the apex of each U-shape fold, two of aid projections,one entering each of said openings, and said openings and saidprojections lying on a line parallel to said linear lengths andextending axially of each U-shape fold at its apex.

3. A support means as defined in claim 2, including insulator blocksfirmly mounted on said supports, and said projections being mounted insaid blocks.

4. A support means as defined in claim 3, wherein said frame comprisesuninterrupted end plates at each end of said resistor at right angles tosaid insulator blocks and extending to predetermined levels above andbelow the ribbon of said resistor, said insulator blocks extending fromend plate to end plate to provide substantially uninterrupted walls onside adjacent and just outside said U-shape folds, and said blocksterminating at said predetermined levels, whereby a plurality of saidsupport means may be stacked vertically with said blocks and end platesin registration whereby to provide an open vertical tunnel for forcedventilation.

5. A support means as defined in claim 2, wherein plates are firmlymounted on said supports, and projections are rigid with said plates.

6. A support means as defined in claim 2, wherein plates are firmlymounted on said supports, and projections are integral with said plates.

7. A support means as defined in claim 1, including two of said openingsbeing provided at the apex of each U-shape fold, two of saidprojections, one entering each of said openings, and said openings andsaid projections lying on a line parallel to said linear lengths andextending axially of each U-shape fold at its apex, each of saidsupports comprising a bolt running the full length of said resistor andbeyond said frame end por tions, said insulating means includinginsulator blocks positioned end to end along said bolts, there beingsuitable openings through said blocks to receive said bolts,interengaging means on the engaging ends of adjacent blocks holding saidblocks in registration, interengaging means between the end block oneach bolt and the adjacent frame end portion to provide rigidity,

said projections mounted in said blocks, and nuts threaded on the endsof said bolts and pulled up tight against the outer surfaces of saidframe end portions and holding said blocks and said frame end portionsassembled with said resistor held on said projections, there beinginsulating means between said nuts and said end portions.

8. A support means as defined in claim 1, including two of said openingsbeing provided at the apex of each U-shape fold, two of saidprojections, one entering each of said openings, and said openings andsaid projections lying on a line parallel to said linear lengths andextending axially of each U-shape fold at its apex, a verticallyextending plate opposite each of said U- shape folds, each pair of saidprojections being vertically spaced on one of said plates, there beingtwo of said supports on each side of said resistor, each of saidsupports comprising a bolt running the full length of said resistor andbeyond said frame end portions, there being two openings through each ofsaid plates through which the associated bolts pass, an electricallyinsulating tube surrounding each of said bolts between said frame endportions, said tubes extending through said openings in said plates,hollow spacers surrounding said tubes between said plates and betweenthe last plate on each bolt and the adjacent frame end portion,electrically insulating means between spacers and said plates andbetween said spacers and said frame end portions, and nuts threaded onthe ends of said bolts and pulled up tight against the outer surfaces ofsaid frame end portions and holdin said plates and said spacersand saidframe end po ions assembled with said resistor held on said projections,there being insulating means between said nuts and said end portions.

1. A support means for a continuous ribbon-type resistor fanfolded intoa plurality of equally spaced parallel uniform linear lengths connectedby U-shape folds, comprising a frame having portions at opposite ends ofsaid resistor opposite said linear lengths, supports connected betweensaid frame portions, one support extending crosswise of said fanfolds oneach side of said resistor, there being an opening through said ribbonresistor at the apex of each U-shape fold, projections carried by saidsupports, one projection opposite each of said openings, each of saidprojections being loosely received in its associated opening, meanselectrically insulating said resistor from said supports and from saidframe, and terminals attached to said resistor.
 2. A support means asdefined in claim 1, including two of said openings being provided at theapex of each U-shape fold, two of aid projections, one entering each ofsaid openings, and said openings and said projections lying on a lineparallel to said linear lengths and extending axially of each U-shapefold at its apex.
 3. A support means as defined in claim 2, includinginsulator blocks firmly mounted on said supports, and said projectionsbeing mounted in said blocks.
 4. A support means as defined in claim 3,wherein said frame comprises uninterrupted end plates at each end ofsaid resistor at right angles to said insulator blocks and extending topredetermined levels above and below the ribbon of said resistor, saidinsulator blocks extending from end plate to end plate to providesubstantially uninterrupted walls on side adjacent and just outside saidU-shape folds, and said blocks terminating at said predetermined levels,whereby a plurality of said support means may be stacked vertically withsaid blocks and end plates in registration whereby to provide an openvertical tunnel for forced ventilation.
 5. A support means as defined inclaim 2, wherein plates are firmly mounted on said supports, andprojections are rigid with said plates.
 6. A support means as defined inclaim 2, wherein plates are firmly mounted on said supports, andprojecTions are integral with said plates.
 7. A support means as definedin claim 1, including two of said openings being provided at the apex ofeach U-shape fold, two of said projections, one entering each of saidopenings, and said openings and said projections lying on a lineparallel to said linear lengths and extending axially of each U-shapefold at its apex, each of said supports comprising a bolt running thefull length of said resistor and beyond said frame end portions, saidinsulating means including insulator blocks positioned end to end alongsaid bolts, there being suitable openings through said blocks to receivesaid bolts, interengaging means on the engaging ends of adjacent blocksholding said blocks in registration, interengaging means between the endblock on each bolt and the adjacent frame end portion to providerigidity, said projections mounted in said blocks, and nuts threaded onthe ends of said bolts and pulled up tight against the outer surfaces ofsaid frame end portions and holding said blocks and said frame endportions assembled with said resistor held on said projections, therebeing insulating means between said nuts and said end portions.
 8. Asupport means as defined in claim 1, including two of said openingsbeing provided at the apex of each U-shape fold, two of saidprojections, one entering each of said openings, and said openings andsaid projections lying on a line parallel to said linear lengths andextending axially of each U-shape fold at its apex, a verticallyextending plate opposite each of said U-shape folds, each pair of saidprojections being vertically spaced on one of said plates, there beingtwo of said supports on each side of said resistor, each of saidsupports comprising a bolt running the full length of said resistor andbeyond said frame end portions, there being two openings through each ofsaid plates through which the associated bolts pass, an electricallyinsulating tube surrounding each of said bolts between said frame endportions, said tubes extending through said openings in said plates,hollow spacers surrounding said tubes between said plates and betweenthe last plate on each bolt and the adjacent frame end portion,electrically insulating means between spacers and said plates andbetween said spacers and said frame end portions, and nuts threaded onthe ends of said bolts and pulled up tight against the outer surfaces ofsaid frame end portions and holding said plates and said spacers andsaid frame end portions assembled with said resistor held on saidprojections, there being insulating means between said nuts and said endportions.